PIC18F258 MICROCHIP [Microchip Technology], PIC18F258 Datasheet - Page 181

• Manufacturer Part Number: PIC18F258
• Description: High Performance, 28/40-Pin Enhanced FLASH Microcontrollers with CAN
• Manufacturer: MICROCHIP [Microchip Technology]

17.4.17.2
During a Repeated START condition, a bus collision
occurs if:
a)
b)
When the user de-asserts SDA and the pin is allowed
to float high, the BRG is loaded with SSPADD<6:0>
and counts down to 0. The SCL pin is then de-asserted,
and when sampled high, the SDA pin is sampled.
If SDA is low, a bus collision has occurred (i.e., another
master
Figure 17-29). If SDA is sampled high, the BRG is
FIGURE 17-29:
FIGURE 17-30:
 2002 Microchip Technology Inc.
A low level is sampled on SDA when SCL goes
from low level to high level.
SCL goes low before SDA is asserted low, indi-
cating that another master is attempting to
transmit a data ’1’.
is
SDA
SCL
BCLIF
RSEN
S
SSPIF
SDA
SCL
RSEN
BCLIF
S
SSPIF
attempting
Bus Collision During a Repeated
START Condition
BUS COLLISION DURING A REPEATED START CONDITION (CASE 1)
BUS COLLISION DURING REPEATED START CONDITION (CASE 2)
to
transmit
SCL goes low before SDA,
Set BCLIF. Release SDA and SCL.
a
data
Preliminary
’0’,
T
BRG
Sample SDA when SCL goes high.
If SDA = 0, set BCLIF and release SDA and SCL.
reloaded and begins counting. If SDA goes from high to
low before the BRG times out, no bus collision occurs
because no two masters can assert SDA at exactly the
same time.
If SCL goes from high to low before the BRG times out
and SDA has not already been asserted, a bus collision
occurs. In this case, another master is attempting to
transmit a data ’1’ during the Repeated START
condition, Figure 17-30.
If, at the end of the BRG time-out both SCL and SDA
are still high, the SDA pin is driven low and the BRG is
reloaded and begins counting. At the end of the count,
regardless of the status of the SCL pin, the SCL pin is
driven low and the Repeated START condition is
complete.
T
Cleared in software
BRG
PIC18FXX8
Interrupt cleared
in software
'0'
'0'
DS41159B-page 179
’0’